1. Technical Field
The present invention relates to semiconductor fabrication and more particularly to methods and devices for applying contacts to sub-lithographic features in integrated circuits.
2. Description of the Related Art
As optical lithography approaches the end of its extendibility, other options have been proposed for defining increasingly-small features. Sidewall Image Transfer (SIT) has been set forth as one method for making sub-lithographic features. SIT utilizes spacers on lithographically-printed “mandrels” as image-defining shapes. Since two spacers are available for each lithographically-defined image (one on each side), SIT in its simplest form, “frequency doubles” what would be achievable employing the lithography to fabricate mandrel patterns.
One problem with “useful-width” sub-lithographic patterns, however, is that it is difficult to make contact to them. Individual contacts need to be printed using the best-available lithography. The minimum size printable with a lithography generation is “F”, which is presumably the same dimension as employed for mandrel printing.
With frequency-doubled (standard) SIT at minimum pitch, a (1F) contact is landed on a line that is (approximately) F/2 having only F/2 spaces to adjacent lines. Landing a contact on anything smaller is extremely difficult.
The usefulness of SIT is limited if connections between improved-pitch lines and surrounding circuits cannot be made. Though, for arrays of lines such as for memory arrays, where long connections are possible, the improved pitch may be valuable for the “array” even when support areas are defined using standard lithography.